DESCRIPTION: We are working to establish the regulation of PITX2 expression, transcriptional activities and protein interactions that modulate PITX2 function during tooth morphogenesis. PITX2 provides a unique tool for studying the molecular control of tooth formation since it is selectively expressed at the earliest stage of tooth development. Our work on PITX2 mutations associated with Axenfeld-Rieger syndrome (ARS) has provided a molecular basis for tooth anomalies in these patients. However, we have only begun to understand the molecular mechanisms of PITX2 and its role in tooth development. Our overall goal is to understand the coordinated control of tooth development by the cascade of transcription factors, which starts with PITX2. Therefore, the focus of this proposal is to understand the target genes that are activated by PITX2 and identify PITX2 interacting factors that temporally and spatially modulate its transcriptional activity. Based on our continuing research and previous results we know that PITX2 specifically regulates the expression of several genes during tooth development and PITX2 isoforms differentially modulate gene expression. We have identified factors that act in concert with PITX2 to fine tune the expression of these genes. We propose to test our hypothesis that PITX2 isoforms differentially regulate gene expression through specific 3rotein-protein interactions. Newly identified PITX2 C-terminal mutations associated with ARS patients will provide new mechanisms for the dental anomalies in these patients. We will compare the activities of these F_ITX2mutants to wild type in order to identify factors and PITX2 transcriptional activities required for normal gene expression. We will test our hypothesis that phosphorylation regulates proteins interacting with either the PITX2 N-terminal or C-terminal regions. Our recent identification of a chromatin remodeling factor that directly binds the PITX2 C-terminal tail will be a focus of our studies. We will test our hypothesis that the transcriptional activity of PITX2 is tightly regulated during development by its interaction with this factor. This research will provide a mechanism for how a developmental regulated transcription factor accurately activates its target gene in a sea of chromatin and other factors during the highly regulated phase of tooth development during embryogenesis. These studies will provide the foundation for a better understanding of the molecular control of early tooth development.